"This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of extreme trans-Neptunian objects and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto," said Carlos de la Fuente Marcos, scientist at the Complutense University of Madrid.

There could be at least two unknown planets hidden well beyond Pluto, whose gravitational influence determines the orbits and strange distribution of objects observed beyond Neptune. This has been revealed by numerical calculations made by researchers at the Complutense University of Madrid and the University of Cambridge. If confirmed, this hypothesis would revolutionise solar system models.

Astronomers have spent decades debating whether some dark trans-Plutonian planet remains to be discovered within the solar system. According to the calculations of scientists at the Complutense University of Madrid (UCM, Spain) and the University of Cambridge (United Kingdom) not only one, but at least two planets must exist to explain the orbital behaviour of extreme trans-Neptunian objects (ETNO).

The most accepted theory establishes that the orbits of these objects, which travel beyond Neptune, should be distributed randomly, and by an observational bias, their paths must fulfil a series of characteristics: have a semi-major axis with a value close to 150 AU (astronomical units or times the distance between the Earth and the Sun), an inclination of almost 0° and an argument or angle of perihelion (closest point of the orbit to our Sun) also close to 0° or 180°.

Yet what is observed in a dozen of these bodies is quite different: the values of the semi-major axis are very disperse (between 150 AU and 525 AU), the average inclination of their orbit is around 20° and argument of Perihelion -31°, without appearing in any case close to 180°.

"The exact number is uncertain, given that the data that we have is limited, but our calculations suggest that there are at least two planets, and probably more, within the confines of our solar system," adds the astrophysicist.

To carry out the study, which is published as two articles in the journal 'Monthly Notices of the Royal Astronomical Society Letters', the researchers have analysed the effects of the so-called 'Kozai mechanism', related to the gravitational perturbation that a large body exerts on the orbit of another much smaller and further away object. As a reference they have considered how this mechanism works in the case of comet 96P/Machholz1 under the influence of Jupiter.

Despite their surprising results, the authors recognise that their data comes up against two problems. On the one hand, their proposal goes against the predictions of current models on the formation of the solar system, which state that there are no other planets moving in circular orbits beyond Neptune.

However, the recent discovery by the ALMA radio telescope of a planet-forming disk more than 100 astronomical units from the star HL Tauri, which is younger than the Sun and more massive, suggests that planets can form several hundred astronomical units away from the centre of the system.

On the other hand, the team recognises that the analysis is based on a sample with few objects (specifically 13), but they point out that in the coming months more results are going to be published, making the sample larger. "If it is confirmed, our results may be truly revolutionary for astronomy," says de la Fuente Marcos.

Last year two researchers from the United States discovered a dwarf planet called 2012 VP113 in the Oort cloud, just beyond our solar system. The discoverers consider that its orbit is influenced by the possible presence of a dark and icy super-Earth, up to ten times larger than our planet.

Carlos de la Fuente Marcos, Raúl de la Fuente Marcos, Sverre J. Aarseth. "Flipping minor bodies: what comet 96P/Machholz 1 can tell us about the orbital evolution of extreme trans-Neptunian objects and the production of near-Earth objects on retrograde orbits". Monthly Notices of the Royal Astronomical Society 446(2):1867-1873, 2015.

We've known of two proto planets beyond or intersecting the Pluto/Charon mutual orbiting "sub planet" system. We know Jupiter was much closer to the sun at one time and played havoc with the inner planets and asteroid bodies causing likely the "late bombardment" period of the inner planets...then due to orbital mechanics and moving gravity interplay with the large gas planets, we assumed Jupiter supposedly attained its present orbit on the other side of the asteroid belt...or helped form or indeed formed like herding sheep, the asteroid belt...we're not sure yet and theories conflict. Anyway, between Pluto/Charon and the actual Oort belt I would have to assume there are proto planets or in fact planet sized bodies which were flung hither by gravitational mechanics of the large gas planets or Jupiter's meandering orbital path early on in the Solar system's history. There was so much going on that it's hard to nail down what exactly happened. One theory states and with some proofs that another star system, likely one of our sun's "sister" suns formed from the same nebula star birthing grounds, brushed close enough to our system to either exchange material or seriously disrupt things gravitationally. in both sister star systems.

Ideas and theories abound and always will as mankind strives to understand how things worked and still work and what event collection brings us to today's reality. One must of course be flexible to withstand the constant dynamics of discovery and be exited about news yet poke just a little tongue in cheek, or as a metaphoric phrase, I always hover a cube of suger's worth of doubt over the pitcher of knowledge lemon aid

So to summarize don't be surprised with discoveries, as technology and toys advance, that we find some really interesting new stuff not only on and around our inner planets and moons thereof, but on this side of, and yet beyond and deep inside the Oort realm. Astronomy as a "real" science is pretty new, i.e. the actual study of it, not just looking through a primitive refractor telescope or star gazing aboard a boat for guidance. So being "pretty new", naturally we are to expect a high degree of discovery (as with all sciences which have flowered in the last two centuries).